In recent years, attention has been given to hybrid vehicles and electric vehicles with environmental issues as a background. These vehicles employ an electric motor as a drive power source, and a power storage device such as a secondary battery is used as an electric power supply thereof.
A technique for charging such a power storage device mounted on a vehicle by an external electric power supply has already been proposed. For example, Japanese Patent Laying-Open No. 8-65815 has disclosed an electric automobile charge control device that controls charging of an onboard battery by a charger supplied with an external power. This control device includes instructing means for instructing preferential driving of an onboard electric load. Further, the control device includes means for driving the onboard electric load by the charger when it detects an instruction from the instructing means to perform preferential driving of the onboard electric load during the operation of charging the onboard battery.
The electric vehicle disclosed in Japanese Patent Laying-Open No. 8-65815 has a structure in which a battery is always connected to a charger. Therefore, the battery is continuously charged during an operation of an onboard electric load (more specifically, an electric air conditioner) so that the battery may be overcharged. Japanese Patent Laying-Open No. 8-65815 has disclosed that the charging of the battery ends when it is determined that the battery is fully charged, during the operation of the onboard electric load. However, it is preferable to use a plurality of different methods, for preventing the overcharging of the battery more reliably.